1. Field Of The Invention
The present invention relates generally to commercial refrigeration, and in a more particular sense has reference to refrigerated display cases of the type used in food markets.
There are many basic types of refrigerated display cases, and in one sense, all of these cases can be divided into two broad categories: (a) those in which the customer access openings are normally closed by doors, known in the industry as "reach-in" cases; and (b) those in which the access openings are uncovered during normal store hours, with the access openings being either in the top or in the front of the cases.
The present invention relates to the second category. Within this category, again there are various types of cases, including open top and open front cases. The present invention relates to those categorized as open top cases, and in a more specific sense, relates to those cases of the open top type known as "wide island" display cases, wherein two side-by-side product display wells open upwardly and have a longitudinally and centrally extending partitioning structure. Cases of this type, during refrigeration cycles, have air flow patterns individual to the separate product wells, with air generally flowing completely around the sides, bottom, and across the open top of each well. Often, wide island cases have their individual product wells refrigerated to different temperatures, that is, one side of the case may be refrigerated to a temperature designed to properly maintain ice cream, while the other may be refrigerated for holding frozen foods, in a typical installation.
2. Description of the Prior Art
Refrigerated display cases, including those of the wide island, open top type, are typically defrosted in one of three ways, namely, electrical, hot gas, and air. The first approach utilizes electrical resistance heaters strategically placed to assure defrosting of the evaporators when the defrost cycle is initiated. The second utilizes a system of valved piping through which hot, compressed gaseous refrigerant is directed from the outlet side of the compressors, for flow in a reverse direction through the evaporator or evaporators being defrosted. The third arrangement utilizes air drawn from the ambient atmosphere surrounding the case, the air being caused to flow through the ducting through which refrigerated air is circulated during the refrigeration cycle, so as to flow through the evaporators.
Each approach has advantages and disadvantages. Electrical defrost is highly efficient, but may involve a high energy cost, particularly in geographical areas where electrical energy comes at a high price.
The hot gas system disclosed in patents such as U.S. Pat. Nos. 3,905,202 to Taft et al or 4,151,722 to Willitts et al, is highly effective, but is not favored by some users who believe that the efficiency of this system is outweighed by a higher initial cost and subsequent servicing requirements.
There is, too, what might be considered as a sub-classification of the hot gas defrost system, in which defrosting is effected by so-called "cool gas." In this arrangement, exemplified by U.S. Pat. No. 3,427,819 to Seghetti and U.S. Pat. No. 4,167,102 to Willitts, saturated gaseous refrigerant is circulated through a piping system similar to that used in hot gas defrost.
Air defrost, in which the means for melting frost from the evaporators is ordinary ambient air, has an obvious advantage over the other methods, in that it does not require electrical resistance devices as the primary source of heat to be applied to the evaporators, nor does it require special piping or valving above and beyond that needed during the refrigeration cycle. It does have disadvantages, however, in that the defrost cycle may be over-long, or alternatively, there may be excessive heat exchange between the refrigerated food products and the ambient air used for defrost purposes, causing the temperature of the food products to be elevated to an undesirable extent during the defrost cycle.
Accordingly, prior art patents that have concerned themselves with the use of ambient air as the defrosting means have sought to minimize the length of the defrost cycle as well as the effect of the ambient air upon the refrigerated food products. The challenge becomes particularly significant in cases of the open front or open top type, and even more so in wide island, open top cases. This is so because in a wide island case, the defrost air pattern for one side of the case may affect or be affected by the defrost air flow pattern at the other side. Also, it is difficult to provide a continuing fresh supply of ambient air for both sides of a wide island case. Still further, in some wide island cases, refrigeration at one side is produced at a temperature different from that of the other side, presenting special problems in the length of time required for the air defrost cycle when both sides are being simultaneously defrosted.
Continuing efforts have been made in the art to increase the efficiency of air-defrosted wide island cases. Typical among the patents that have been granted in this category are U.S. Pat. Nos. 4,182,130 to Ljung; 4,337,626 to Ibrahim; 4,304,098 to Rydahl; 4,314,457 to Ibrahim; and 4,337,626, also to Ibrahim.
All of these patents have approached the problems inherent in providing air defrost for wide island cases, by utilizing arrangements wherein both sides of the wide island case must be refrigerated to the same temperture, and/or heat exchange between the opposite sides of the cases during refrigeration is not appreciably reduced and indeed in some instances is increased. While a heat exchange between the opposite sides of the case, tending to equalize temperatures therebetween, is not a problem when both sides are being refrigerated to the same temperature, it is obviously undesirable when, for example, one side is to hold frozen foods and the other side is to hold ice cream, with the maintained temperatures of the product display spaces being of necessity at different levels.
It is, accordingly, one object of the present invention to provide a wide island case of the air defrost type, wherein in one form of the invention in which the opposite sides of the case are maintained at different temperatures when in a refrigeration mode, both sides can share, simultaneously, a common defrost cycle.
Another important object of the invention is to provide a case of the type described wherein the defrost cycle will be held to a desirably low length.
Yet another object is to provide a case as described in which the refrigerated food products will be effectively protected during the defrost cycle.